Re: [PATCH v4 2/3] arm/efi: Use dom0less configuration when using EFI boot

[Jan Beulich <jbeulich@xxxxxxxx>]

On 01.10.2021 17:13, Luca Fancellu wrote:
> 
> 
>> On 1 Oct 2021, at 15:22, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 01.10.2021 15:55, Luca Fancellu wrote:
>>>> On 1 Oct 2021, at 12:02, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>>> On 30.09.2021 16:28, Luca Fancellu wrote:
>>>>> @@ -1361,12 +1361,30 @@ efi_start(EFI_HANDLE ImageHandle, 
>>>>> EFI_SYSTEM_TABLE *SystemTable)
>>>>>        efi_bs->FreePages(cfg.addr, PFN_UP(cfg.size));
>>>>>        cfg.addr = 0;
>>>>>
>>>>> -        dir_handle->Close(dir_handle);
>>>>> -
>>>>>        if ( gop && !base_video )
>>>>>            gop_mode = efi_find_gop_mode(gop, cols, rows, depth);
>>>>>    }
>>>>>
>>>>> +#ifdef CONFIG_HAS_DEVICE_TREE
>>>>> +    /* Get the number of boot modules specified on the DT or an error 
>>>>> (<0) */
>>>>> +    dt_modules_found = efi_arch_check_dt_boot(dir_handle);
>>>>> +#endif
>>>>
>>>> So I had asked to add a stub enclosed in such an #ifdef, to avoid the
>>>> #ifdef here. I may be willing to let you keep things as you have them
>>>> now, but I'd like to understand why you've picked that different
>>>> approach despite the prior discussion.
>>>
>>> There must be a misunderstanding, your message in the v3 was:
>>>
>>> "Every time I see this addition I'm getting puzzled. As a result I'm
>>> afraid I now need to finally ask you to do something about this (and
>>> I'm sorry for doing so only now). There would better be no notion of
>>> DT in x86 code, and there would better also not be a need for
>>> architectures not supporting DT to each supply such a stub. Instead
>>> I think you want to put this stub in xen/common/efi/boot.c, inside a
>>> suitable #ifdef.”
>>>
>>> So I thought you wanted me to remove the stub in x86 (since it doesn’t 
>>> support DT)
>>> and put this call under #ifdef so it won’t be compiled for arch not 
>>> supporting DT.
>>
>> So FTAOD I'll repeat the crucial part: "I think you want to put this
>> stub in xen/common/efi/boot.c". There was nothing about removing the
>> stub altogether.
> 
> Oh ok, now I see, so in your opinion this is a better idea:
> 
> #ifndef CONFIG_HAS_DEVICE_TREE
> static inline int __init efi_arch_check_dt_boot(EFI_FILE_HANDLE dir_handle)
> {
>     return 0;
> }
> #endif
> 
> But I would like to understand the advantage respect of my approach, could you
> explain me?

Well, to a degree it's a matter of taste. Your approach may lead to a long
series of various #ifdef sections in a single function, harming readability.
Having stubs instead (usually placed in headers, albeit not in this case)
allows the main bodies of code to remain more tidy.

Jan